The present invention relates to a de-clutch mechanism for coupling a rotatable driven load member to a secondary drive and decoupling the power drive when the primary drive is inactive, and for disconnecting the secondary drive and automatically connecting the power drive when the primary drive is actuated. The primary drive is typically a power drive while the secondary drive is ordinarily a manual handwheel drive.
While a de-clutch mechanism of the type here involved may have other uses, the mechanism is particularly suited for use in valve operators. Valve operators are power driven operating mechanisms used for opening and closing large valves. In such cases, the rotatable member which is to be driven by either the primary or secondary drive, is an internally threaded drive sleeve or nut which, when driven rotationally, moves an externally threaded valve stem in one axial direction or the other, thereby to move the valve toward its open or closed position. The drive sleeve or nut is typically driven by a worm gear driven by a power driven worm shaft.
If, for adjustment or maintenance purposes, or in the event of a power failure, or for any other reason, it is desired to rotate the drive sleeve manually, as by a handwheel, while the power is off, a de-clutch mechanism must be provided for shifting the drive from power drive to manual drive, and for returning the drive automatically from manual to power drive means when the power is available.